On large and dangerous game where the extra power would be useful it is usually better to get a bigger hole in the barrel.I think one would be hard pressed to improve the 375 H&H, thats an oxymoron...it cannot be improved. 
------------------
Ray Atkinson
The .375 H&H improved is the same old trick that everyone has been using since the turn of the century. They just move the shoulder forward and blow the case out more. By that simple expedient the case has more capacity.
Whereas the .375 H&H holds 96.37 water grains, it's length from base to shoulder is 2.353" and it's sholder angle is (deg's/side 7.95 )
The .375 H&H improved holds 104.77 water grains, it is 2.464" from base to shoulder and its shoulder angle (deg's side is 40.51 )
The .375 Weatherby holds 104.59 water grains it's length to shoulder is 2.37" and it has a convex Weatherby shoulder. Weatherby cases can be nmade from .375 H&H cases.
What's the difference? If you like to tinker in your shop, they can be fun and amusing shaping and fireforming cases.
Kendall
Brad Amundson
As someone who has actually used a 375 improved since 1979, I can tell you it is a killer.
Anyone who thinks its the same as a 375 H and H has not used one or the other side by side on the same animals with the same bullets.
I have always used nosler or better bullets, so the extra velocity is no problem.
A 250 gr at 3050 fps or 275 gr at 2975 fps or 300 gr at 2800 fps makes a bigger hole than the same bullets from the std case.
this causes loss of concisounsness sooner than the slower std 375.
No mystery here.
this is based on some 500 head killed.
If you dont believe me ask Saeed, our moderator who has similar ballistics from his 375 x 404.
Saeed used the barnes I use the bitterroot. Barnes has no frontal area after petals blow off, and Bitterroot expands to an inch dia with 95% weight retention even at point blank range. Both appear to work.
Youll love the 375 improved.
Andy
Sounds like you have a burr under your saddel pardner. You have misse some of my posts.
I said I was 5th generation, I have hunted for over 25 years, have taken almost every North American big game type, I have owned too many rifles over the years, buy, sell, trade and presently have a dozen rifles and half a dozen handguns plus a few shotguns. Some of the rifles I do own are very special, some of the older models are collectors category but shoot.
I see game every day. As soon as the snow hits the mountains there will be 10,000 elk at the feeding grounds plus several hunderd buffalo ( bison ). And some antelope will be around.
I can go out and see moose, mountain goats, Big horns, cougars and bears any time I feel like taking a hike, not to mention mule deer around like rabbits and whitetails, coyotes sage grouse, and a few other animals..
I've already "popped" a few species this season while you were just thinking about it.
What's the point in getting on the internet and bragging. 90% of what is posted is suspect! Some of it is just outrageous. And some dupes are gullible enough to swallow it hook, line and sinker.
As regards experience in shooting, my views differ quite a bit from those of many individuals who post. Whereas some wax eloquent about one caliber versus another and x number of feet per second, or Joe Doaks fancy bullet being better than Rastus Browns bullet; - I just don't buy into it. It's hype, sales gimmickry.
All it takes to successfully hunt is a rifle of appropriate size. That rifle must be able to shoot all the way through any animal. I don't care if it is a pure lead ball, or all copper - it works. I don't care if it is a flint lock, a muzzle loader, a hand gun, a shot gun or a breach loader, it will do the job.
I got engaged in some philosophical exchanges with several posters and the only result was that all of them got their nose out of joint and bugged out. Who needs that aggravation. Everybody has his own opinion.
Speaking of opinions, - lets hear from YOU. Lay it on us. Tell us all about yourself and how many animals you have taken with your arsenal.
We're all ears. The stage is YOURS. Go for it.
Kendall
With the advent of factory-loaded .375 Weatherby ammo, this caliber is a much more viable proposition for African use than it ever was before. It would appear as though the .375 Dakota would fill the bill in approximately the same manner. The headstamps are correct, and with todays high-quality bullets, etc., the .375 Weatherby or Dakota would make a lot of sense for the guy who wants more power than is offered by lesser .375's, but without the heavy recoil of the .378 Weatherby.
I'd go for one of these chamberings myself, but I have a good .375 H&H right now that I have no intention of messing with or getting rid of, and besides, I can always grab my .416 Remington if I need more horsepower.
AD
Sarge
Most of the critters Ive shot with 375 imp have been feedlot cattle and american bison at close range where bullet failure would be obvious. Since they were butchred on the spot could also see wounds as well as a veterinarian's necropsy.
the extra velocity makes quite a difference!
Also shot 22 elk.
My imp has a 25 degree shoulder.
One advantage of this case is that you can still shoot std 375 ammo, and when loaded with IMR 4831 you get that high velocity from a 22 inch barrel at very very modest pressure. You literally cant stuff enough 4831 into the case to get into trouble. I dont completely trust double base powders necessary to get high vel from the std case.
Sarge, what powder are you using, and what barrel length???
I would not change either if I was doing that good.
The debate about improving the 375 has always puzzled me, since most of us would not think twice about shooting a 30-06 instead of a .308 or a 300 h and h vs a .30-06 and that is pretty much the difference.
RL-15 and W-760 make it possible to ring out some extra vel from the old girl but I like 4831.
Andy
While I have to agree with Ray that slower is better for Dangerous game, it seems to be one of the primer dual purpose guns.
Since many of us will likely hunt more large plains game or bears then buff and elephant, it seems to be a slightly more practical gun.
I share your enthusiasm about the .375 H&H Improved, in fact so much so that I am currently having a Ruger #1 built in the Ackley version (40� shoulder).
I'd be curious to hear about some specifics of some of you pet loads, just so I have a starting point.
Thanks
-Mr Mike
I had my .375 H&H rechambered and it made a very strange looking cartridge case after fireforming. This was the short reamer. I traded some original Norma cases to a gent in Nebraska who sent me two boxes of fireformed Winchester brass. It was .77 inches too long. My 'smith finally got things straightened out with his reamer supplier and it is now correct. I checked one of my cases against current Weatherby production and it is correct. The correct dimensions can be found in A-Squares manual.
I think I am going to buy a factory Weatherby. This year they are going to offer a fibermark in this chambering.
I want to get a gun that is not too expensive to see how I like the caliber before I get too invested into it.
The differnt size of chmabers is one of the resons I have steered clear of rechmbering jobs thus far. Don't feel I know enough to have it done just yet.
Thanks for the advice
I like the 375 Weatherby. I had one built in 1986 with the reamer Willis Fowler of Anchorage, Alaska had, and it worked well with the off the shelf RCBS dies available then. It is a Mark X Interarms Mauser barreled action (24" factory barrel) in 375 H&H rechambered to 375 WBY. Parkerized then matte blued. Brown Precision fiberglass stock pillar bedded.
A Ruger No. 1 quarter rib was attached to the barrel for rear sight and scout scope mount function (with 2 3/4 X Burris Scout Scope). A custom Weaver style two piece scope base set up was made to fit a 4X Leupold onto the action with 3 Weaver rings, two in the front and one in the rear position. 8 X 40 screws. A pop up peep on the rear Weaver base. Hooded ramp front sight.
My load was a mild one of 88 grains of IMR 4350 with 300 grain Swift bullets of the old vintage that weren't as accurate as the current Swifts. It shot them into 1 1/2 MOA at 2700 fps.
I carried the rifle to Kodiak and killed running deer at 150 yards with it and other deer at 50 to 200 yards. I did chase after King Kong of Kodiak and got to within 300 yards of him, but did not risk a shot at what looked like a 13 foot square bear... 
... He got away from this self guided resident hunter in Kaguyak bay, southwest Kodiak Island. But, I was fearlessly well armed with the 375 Weatherby.
My Botswana safari was with a 375 H&H and 416 Rigby. That is the power range needed for any game on the planet.
Until they make a 396 BAM (Bwana's All-around Magnum), I think the best solution utilizing the KISS principle is to go with the improved 375, and the 375 Wby may be the most sensible of all, because you can still fire standard 375 H&H loads in it and only lose 150 fps in the improved chamber.
Another alternative is to go with Saeed's 375/404 or the 375 RUM. One bullet weight for everything: 300 grains. KISS principle.
Bring the second rifle in the same chambering for the backup KISS. Is this what all of Saeed's experience has taught him? A lesson I have learned here.
I would have to agree whole heartedly with Andy on this one.
------------------
Good huntin', shootin', and spear chuckin',
RAB
He is a graduate of the Colorado School of Trades Gunsmithing Program. A decent smith. He wrote a slim volume on rebarreling rifles, published by Wolfe. He was a bit of a curmudgeon, but did good work for me. He always tried to turn my sows' ears into silk purses.
------------------
Good huntin', shootin', and spear chuckin',
RAB
[This message has been edited by R. A. Berry (edited 10-07-2001).]
On the up-side, if you stay with loads similar in speed to before improving, pressure will be less and recoil comes down. Very few of us may be interested in that, but the fact is there for the taking. Pushing up speed will increase the performance of the cartridge as far as external ballistics are concerned and, simply put, will make the rifle shoot flatter, with less wind drift and a shorter time of flight. This in turn allows more accurate placement of the bullet under all circumstances and removes some of the guesswork from the situation.
As far as terminal ballistics are concerned, the extra power available can be applied in two ways. It can be used to tear the bullet to pieces, or it can be used to improve the ability of the bullet to kill. Should one choose to go down the path of more speed, the choice of bullet becomes more important. Regardless of the opinion of some, there are bullets that will get the job done under a given set of parameters, and bullets that will not be up to the task. The old adage of "Use enough gun" is also true when applied as "Use enough bullet".
Hunting is a contest between you and your quarry. You bring a package into the contest consisting of your skills and your equipment. If the total sum of this package is in any way inadequate for the task, you lose. When you lose, there is a bill to be paid. If it is as simple as a missed shot or no shot taken at all, no problem, but a wounded and lost quarry, or a buff or ele coming in to check you out is more serious.
It is wise to consider all aspects of the package you take into the contest as it will only perform as well as the weakest link. Considering the package is half the fun anyway.
------------------
Gerard Schultz
GS Custom Bullets
What I found most interesting was the idea of loading the .375 Improved/Weatherby to .375 H&H ballistics. Thereby getting the same speed with less pressure than the original .375. Is that valid? I had assumed that you would probabely lose velocity going with a the same amount of powder in a bigger case. Or are you saying using as much powder as is necessary to obtain the original ballistics? How does that work?
Thank you, Matt.
------------------
Gerard Schultz
GS Custom Bullets
This would mean that pressure has a more substantial effect on recoil than does the amount of powder burned. Most interesting.
Thank you, Matt.
Here is my load for 374 improved wih 25 degree shoulder in blown out WW cases with 215 mag primer, 22 1/2 icnh stainless (atkinson) barrel.
300 gr, 90 gr IMR 4831, 2775 fps, 92 gr 4831, 2825 fps,
275 gr, 94 gr 4831, 2975 fps (full cae, needs fire formed case and drop tube!), low pressure.
250 gr, 85 gr 4064, WW 120 LRP, 3050 fps, low pressure.
Listen up folks, most impressive kills on 1,600 lb - 2,300 lb bison, 250 gr, 275 gr, 300 gr in that order.
Velocity and frontal area kills.
100's killed.
All the rest is conventional wisdom (BS).
Andy
------------------
'Trapper'
We have waited since 10/06 for you to post your bio-data and experience. I would politely ask you again to please favor us with a courteous response. Thanks.
Matt in Virginia:
I've read several of the replies to your inquiry about the .375 H&H Improved and there seems to be quite a bit of meandering about as regards pressures and powders.
Lets look at the facts:
A .375 Improved is a .375 H&H Magnum case that has the shoulder pushed forward and it's angle sharpened. That results in changing the Full case capacity ( full to the top of the neck ) from 96.37 water grains to 104. 77. What it doesn't do is lengthen the case. In fact it actually shortend it from 2.85" to 2.83". At first blush it sounds like a lot more powder. But that is far from the fact.
When a 300 grain Nosler partition bullet is loades a portion of it takes up space inside the case. That space can't be used for powder. The exact amounts of utilizable space are: .375 H&H Magnum 86.732 grains powder. In the .375 H&H Improved it is 88.602 Grains powder.
Effectively you have spent a lot of money to gain less that 2 grains of powder capacity.
The resulting effect is that if you use IMR 4320 the optimum load density will be 81.7% for a chamber pressure of 45,289 psi in the .375 H&H Magnum and it will be also 81.7% load density in the Improved for a chamber pressure of 45,269 psi. We are talking about 20 psi less in the Improved!
Since th maximum case capacity in the .375 Improved is 88.602 grains, if it is loaded to the max you will be running about 57,000 psi chamber pressure.
If you load 90 grains, as suggested above, it will be necessary to severely compress powder. And that will result in a chamber pessure of 58,862 psi. That is considered High pressure.
Trajectory results using a 300 grain bullet will be, loading recommended load density: 2,313 FPS for the.375 H&H Magnum which, if zero ranged at 200 yards, will shoot -5.02" low at 250 yards. The .375 Improved will shoot 2,330 fps ( a gain of 17 fps ) and it will be -4.95" low, a gain of 0.07"
Many suppositions and assumptions that are apparently "presumed" about so called "improvement" in actuality are so marginal that they provide very little in actual enhanced performance. That makes it necessary, to run risks and load up in the danger zone to squeeze out a little bit of performance.
It is far better to simply go to a bigger case of another designation.
Kendall
I'm of the conviction that to improve the killing power of the 375 one must go to a wider cross section of bullet, which would be the 416, 404 class of cartridge. I feel the same about the 458 Vs. 460 Wby, I would go to the 500 for more killing power on big stuff not the 460...MHO
I'd be happy to hunt Buff, Lion or elephant with any of them, but I would use a solid for Buff and elephant with the 375 H&H and slow the 375 Imp. Down to 2400 FPS, in this instance as velocity is the demon of stright penitration in elephants...
------------------
Ray Atkinson
Mr. Tibbe,
What you stated assumes the bullet will be seated the same depth in the case. I know with my .375 Weatherby I can seat the bullet out 'till it almost falls out of the case. Consequently we must take into account this factor. Besides, using a relatively fast burner like 4320 will shoot the pressures up. I will be loading mine with H-4831sc which is slower than RL-19 yet just a touch quicker than RL-22. This will give me a good bracket according to what I see in A-Sq's manual.
Andy,
Now I beg to differ. Not all conventional wisdom is BS. 
Also, your statement that velocity and cross sectional area are the killer factors is too simplistic. At some point bullet weight and bullet construction figure into the equation. However, this equation is the one that is impossible to express. So, we do what works, by conventional wisdom (based on years of field trials and general use by the masses), or by field trials of our own, as in your case of shooting bison and cattle.
------------------
Good huntin', shootin', and spear chuckin',
RAB
You are one cagey cuss. Slipperier than a pumpkin seed. Your bullets sure do have to make a LONG jump to the rifling, pardner. They have a good running start.
Roger says; " I allus load Mah bullets 1/2" to 3/4" offun thuh riflin", "That'a way they git a motorin afore they hit them riffles"
If you will give me your gunsmith's mailing address I will send him a ruler, an OAL gauge and a dimensional drawing of a .375 H&H Magnum chamber along with the throat and freebore measurements. But perhaps he may want to build a .375 H&H Magnum - extended/improved/elongated/stretched.
I could also recommend a new and novel innovation. .375 H&H Magnum shoulderless accentuated, improved. This entails blowing out the shoulder completely. It will then be a straight wall case ( like a shot gun shell ). You then insert the bullet in the bore ( hold the rifle muzzle straight down to get the gravity effect ). When you hear the bullet "click" return the rifle to horizontal. Then you insert the case into the chamber with a wadding glued to the top of the cases neck and a "pusher Plate" contact glued to the wadding. The obvious advantage is that you can get more powder into the case. I've never seen it done but it sounds like an "idea".
Kendall
You should see some of these 350 grain Barnes originals loaded so they have just o.1" clearance in the magazine, yet are still not touching rifling. They are very close but still not there.
I have the .375 here in Fairbanks with me and lots of cases to be fireformed...still. I broke the front sight blade during the shipping to 'smith and back and have some more blades. I just need to put one in and shoot some groups.
I like the muscular looks of the .375 Weatherby. Turns me on you know?
------------------
Ray Atkinson
My 375 improved with 25 degree shoulder, 2.83 case length and WW brass has 105.7 gr water capacity. This compares to 104.5 for the Weatherby and 96.3 for the standard case. (Last two figures from Barnes manual).
The reason the improved case works so well is that you can use a compressed load of 4831. 90 gr is easy for the 300 gr bullet at 3.55 ocl. This produces such low pressure that you have a round edge on your primer and it barely is measurable with a micrometer for case expansion.
The std case using 4831 according to Nosler manual is only 78 gr and this is 99% capacity of case and only 2500 fps.
I have crammed 88 gr 4831 into a std case by seating bullet out to 3.795 inches !!!! which is possible in a Ruger No. 1 which has a very very very long throat. This needed a fire formed case, neck sized only and a drop tube, but velocity from 24 inch tube was 2732 fps.
The improved case is versatile and can be used with 4064 for a reduced load. 77 gr in my barrel giving 2846 fps with a 270 gr.
I like these old fashioned single base (no nitroglycerin) IMR powders. But 4320 and 4064 are way to fast for maximum velocity. The improved case and 4831 go together "like peas and carrots."
Re. "conventional wisdom," the 250, 275 and 300 gr Bitteroot's I used all expanded to about one inch in diameter and held 95-98% weight at point blank range, so the faster you can drive them the larger the mess inside. To put this expansion into perspective, the Swift will expand to 60 caliber.
Since RAB has recent first hand experience with a heart shot buffalo he can fully appriciate this. His perfect shot with the GS FN, which is surely one of the best solids ever made, left the heart intact. A fast medium bore will completely destroy the heart. Nothing left. The 250 and 275 Bitterroot will anyway. The 300 left a couple inches intact, the rest gone. On spine shot the 250 would tear out several inches of spine. That is why I say they were more effective. Because they were!
I still use the 300 gr as my std bullet since I have an improved case and its penetration is consistant from PB to 400 yards. Its trajectory is also the same as 7.62 NATO which Ive shot alot of. If I was still shooting the std case I would use the 250 or 275 Bitterooot.
Anyone here with an open mind who is willing to use a premium bullet and a case full of 4831 will love the 375 improved, JRS, or Weatherby.
BTW, my 375 improved using a 300 gr Hornady FMJ at 2,800 fps will penetrate as well as a 416 Remington with 410 Kynoch FMJ, or the 450 Ackley or 458 x 404 at 2,400 fps with the 500 gr Hornady FMJ. No problem with velocity at all.
All of these bullets shoot through 70-71 3/4 inch boards spaced one inch apart. A std 458 Winchester will do just 58-59 boards and a std 375 61 boards.
I have prtty well disproven the "magic" 2,400 fps business with my latest tests which used 1-8, 1-10, 1-12 and 1-14 twist big bores in boards and water buckets. The 460 weatherby penetrated less in Mike LaGranges tests due to its 1-16 twist.
Like Ralph Nader said (sort of), Velocity kills.
Andy
Surely the 250 grainer would be a more dramatic killer on a heart-lung shot avoiding big bone. That 416 caliber 380 grain FN at 2509 MV passed through a lot of hide, muscle, and bone before getting to the heart, and it went on out the other side.
I think a 300 grain .375 slug at 2700 to 2800 might do just as well, with the right bullet construction: Swift or FN (though the 270 grain FN is the heaviest that exists at GSC...Are you listening Gerard?).
I would have reservations about using a 250 grain expanding bullet of any kind for the humerus busting heart shot on a cape buffalo.
I am definitely not stuck in the 2300-2400 fps rut. I like heavy bullets and high velocity, with the proper bullet construction. .375 caliber or .416 caliber are the most versatile of all.
RAB
------------------
Ray Atkinson
2400 fps and about 600 grains and about fifty caliber is more than enough for anything, and as much as I want to tolerate on the shoulder in a portable brakeless rifle. This is a specialized stopper.
I want to have the higher velocity for long range shooting without having to do too much Kentucky windage and Tennessee elevation. This load must work at closer range on harder targets too. One might have a soft spitzer and a harder bullet of the same weight and velocity shoot to the same POI, or just use a Barnes X. This is a sweet concept. But is it BS?
I think Saeed has proven that 300 grain .375 caliber bullets work reliably at velocities above 2400 fps MV, in the case of the Barnes-X.
I also think that Andy has done extensive testing on penetration media and 500 head of bison and cattle. How can you not give some credence to that? You are not pulling our collective leg are you Andy?
I sure hope Gerard comes to his senses and offers a .375 caliber HV and FN of 300 to 350 grains weight , for those who would use them in the 375 H&H through 378 Weatherby rifles. The 265 grain HV and 270 grain FN are admirable in the 375 H&H, but maybe too light for buffalo and elephant.
How about an HV and FN combo of 335 grains at 2700 fps. The Ultimate. Groundhogs to elephants. KISS principle.
RAB
God Bless America